Electromechanical oscillator circuit



Patented Feb. 25, 1936 PATET ELECTROM'EGHANICAL OSCILLATOR cmoorr Louis A. Gebhard, Washington, D. 0., assignor to Wired Radio, Inc., New York N. Y., a corporation of Delaware Application October 15, 1932, Serial No. 638,011

1 Claim.

My invention relates broadly to high frequency oscillator systems and more particularly to a circuit arrangement for an electromechanical oscillator.

One of the objects of my invention is to providea circuit arrangement for a high frequency oscillator system by which constant frequency oscillations may be sustained accurately under control of an electromechanical oscillator and 1'9 sustained substantially constant over emergency periods even in the event of destruction of the electromechanical oscillator.

Another object of my invention is to provide a circuit arrangement for an electromechanical oscillator having means for sustaining high frequency oscillations either under control of the electromechanical oscillator or independently of such control.

Still another object of my invention is to pro-- vide a high frequency electron tube oscillator circuit arrangement having a negative resistance characteristic with a piezo electric crystal element and a tuning element disposed in circuit with the electron tube oscillator for sustaining oscillations either under control of the piezo electric crystal element or the tuning element.

A further object of my invention is to provide a construction of electron tube oscillator having a plurality of electromechanical vibrators of different frequency characteristics adapted to be electrically connected with the oscillation generation circuit and adapted to control oscillations at selected frequencies, the electron tube oscillator having a negative resistance characteristic.

Other and further objects of my invention reside in the electromechanical oscillator circuits employed in association with a screen grid electron tube as set forth more fully in the specification hereinafter following by reference to the accompanying drawing, in which:

Figure 1 diagrammatically illustrates an electromechanical oscillator circuit embodying my invention; Fig. 2 shows a modified form of electromechanical oscillator circuit arranged according to my invention; and Fig. 3 illustrates a further modified arrangement of electromechanical oscillator circuit embodying my invention.

My circuit includes an electron tube connected with a tunable circuit arranged to impart a negative resistance characteristic to the oscillatory system. This circuit will oscillate over a wide range of frequencies. If a crystal is also introduced in the circuit and the circuit tuned to approximately resonance with the crystal frequency, the crystal will oscillate and take control of the frequency over a limited range of adjustment of the tunable means. If the crystal should fail the circuit will oscillate under the conditions it would without the crystal connected, the frequency of which is governed by the tunable means. If the crystal does not fail but a slightly different frequency is required by selfoscillating action then it may be necessary to disconnect the crystal from the circuit in order to obtain this frequency since at the particular 10 adjustment of the tuning means the circuit may oscillate at the frequency of the crystal instead of the desired frequency if it is not removed from the circuit. The crystal takes control of the frequency of oscillation of the system over a certain 10 range of the tuning means. Over this range the oscillations at frequencies determined by the tuning means are not possible unless the crystal is removed or unless it is rendered inoperative by injury or other means. 211.

In Fig. 1, I have shown a new type of electromechanical oscillator circuit wherein the fourelement tube I is arranged so as to exhibit a negative resistance characteristic. This is done.

by so connecting a potential source that a voltage .5,

is impressed between filament and plate of a screen grid tube with the plate positive: and a still more positive voltage on the screen grid. The grid 2 normally used as the control grid is connected to a source 43, which may be positive,

or it may be connected directly to the filament 3. Reference character 4 designates a by-pass condenser connected between filament 3 and grid 2. Reference character 5 indicates a by-pass condenser connected between cathode 3 and screen 35 grid 6. Piezo electric quartz crystals or other electromechanical oscillators I, 8, 9 and ID of different frequency characteristics are selectively connected by switch I I to an inductance I2 which is included in the plate circuit of tube I as shown. 40 The arm of switch II is connected to inductance I2 through tap I6. When self oscillation is required the switch I I is moved to contact 35. The plate electrode I1 is connected to inductance [2 through tap I8. A tuning condenser I4 is also connected to coil I2 through tap I9. Terminals t5 furnish power to desired output apparatus. If the capacity of condenser I4 and inductance of coil I2 is arranged to be near resonance with the frequency of the crystal the latter will control the 50 frequency of oscillation of the circuit. This control will extend over a considerable frequency band of inductance coil I2 and condenser Hi. If any one of the crystals should fail the circuit may be used as a simple self-oscillation circuit al- 55 though the steadiness and accuracy of frequency will not be as good as with the crystal or other electromechanical oscillator, The power for heating the cathode is obtained from any suitable potential source indicated schematically at 2|]. The power for energizing the plate circuit is obtained from a suitable potential source indicated at 2 I, through tap 22. Connection 23 leads from the potential source for the screen grid 6. A bypass condenser'24 is provided between the plate tap 22 and the ground connection 25.

In lieu of the screen grid tube l, I may-employ a three electrode tube arranged in the oscillator circuit as shown at l in Fig. 2. I have illustrated independent switches for the piezo electric crys-' tals I, 8 and 9 by which the desired crystal is connected in circuit with a selected tap on inductance I2. The inductance I2 is indicated as being provided with taps 26, 2! and 28 independently connected through switches 29, 30 and 3| with piezo crystals I, 8 and 9 respectively. The electron tube has a negative plate circuit connected as described in connection with Fig. 1. The high frequency oscillations generated by the electron tube circuit are delivered to any suitable load through terminals IS. The piezo electric crystals 1, 8, and 9 may be inductively coupled to the coil I2 instead of conductively as shown in Fig. 3 by means of the coil 32 and the other portions of the circuit maintained similar to the arrangements shown in Fig. 1 or 2. The coupling coil 32 is illustrated as having taps thereon similar to the taps illustrated in Fig. 2, the taps being represented at 26, 21 and 28 connected to contacts over which switch'arm 33 selectively operates. Switch arm 33 is electrically connected with switch arm 34 which may be moved over contacts for establishing selective connection with anyone of the piezo crystals 1, 8 and 9. When self oscillation is desired without crystal control the switch 33 1s moved to contact 36 and switch 34 shifted-to'contact 31 or if desired only one switch contact" may be provided. The oscillator circuit has negative resistance characteristics as described in connection with Figs. 1 and 2. The output of the oscillator is delivered to a load circuit at terminals i5 as described with respect to the circuits of Figs, 1 and 2,

It should be noted that it is possible with this system to secure oscillations at a frequency not possible with the crystals at hand by disconnecting the crystal or crystals by opening switch I! and thus securing oscillations with the selfoscillating circuit.

While I have described my invention in certain of its preferred embodiments, I desire that it be understood that modifications may be made and that no limitations upon my invention are intended other than are imposed by the scope of the .appended claim.

What I claim. as new and desire to secure by Letters Patent of the United States is as follows:

An oscillation system comprising, an electron tube having anode, screen, control and cathode electrodes therein, circuit means connected with said electrodes-for producing negative resistance oscillations, said circuit means including a resonant circuit comprising an inductance connected between said anode and said cathode, said resonant circuit being adjustable to different values for cooperating with said tube to" produce and maintain negative resistance oscillations within a wide band of frequencies, a second inductance provided with a plurality of taps connected individually with a plurality of contacts, piezoelectric means selectively connectible with said tapped inductance for selectively causing said oscillations in said wide band of frequencies to be reany selected inductance value, said inductances being inductively coupled and means-for connecting another electrode of each vibrator to one end of said second inductance.

LOUIS A. GEBHARD, 

